1. Field of the Invention
The present invention relates to a method of fabricating a magnetic head slider for use in recording information in a magnetic disk, tape, and the like and playing back the information, and particularly to a method of working on an air bearing surface of a thin film magnetic head slider, which is a component of a magnetic head.
2. Description of the Related Art
A flying magnetic head for use in, for example, a hard disk drive is provided with a magnetic head transducer and a magnetic head slider (hereinafter sometimes referred to merely as "slider"). The slider is a component that flies by the agency of air pressure caused by the magnetic disk rotation so as to keep the magnetic head transducer distanced from the magnetic disk and is provided with grooves (air bearing grooves) on a back surface (air bearing surface) thereof for controlling the air pressure.
As a result of a recording density of the magnetic disk becoming higher in recent years, it is now required that a flying height of the magnetic head from the magnetic disk be reduced. A negative pressure cavity slider as disclosed in U.S. Pat. No. 3,811,856 etc. represents an art meeting such requirement.
The negative pressure cavity slider is structured such that the air pressure occurring on the air bearing surface thereof is precisely controlled by the calculated effect of specifically-shaped grooves formed on the air bearing surface. As a result, variation in the flying height of the magnetic head caused by variation in a linear velocity and skew angle of the magnetic disk is minimal, thereby enabling variation in spacing loss between the magnetic head and the magnetic disk to be minimized.
It was difficult to fabricate the negative pressure cavity slider by mechanical working with the use of a grinder and the like since the air bearing grooves thereof are formed in a complex shape of a curve combined with a plurality of straight lines, unlike conventional linear-shaped grooves called slider rails.
Thereupon, a method of working on the negative pressure cavity slider has been proposed whereby the air bearing grooves are formed thereon with the use of the so called sputter-etching method. In this method, the air bearing grooves are etched on a slider substrate utilizing the effect of sputtering by argon plasma.
For example, an ion beam etching process and ion milling process with the use of a thin film or a photo resist as a mask were disclosed in Japanese Patent Laid-open Publication Nos. 56-74862 and 60-205879. Also, another ion beam etching process with the use of a dry film resist as a mask was disclosed in Japanese Patent Laid-open Publication No. 61-120326. These processes all belong to the sputter-etching method since in an ion beam etching apparatus and ion milling apparatus employed, respectively, in carrying out said processes, the slider substrate is etched by means of ion bombardment by argon ions evolved when plasma excitation of argon gas is caused to occur.
However, there have been pointed out a few problems with such methods as described above relying on the sputter-etching by argon plasma.
A first problem is so called "redeposition" wherein compounds sputtered out of the slider substrate by the ion bombardment are deposited back on the slider substrate again. The "redeposition" has been described in "Electron-Ion Beam Handbook, second edition", p. 487, published by Nikkan Kogyo Shimbun, and also in a number of technical publications.
A typical example of the redeposition is described hereinafter with reference to FIGS. 23A and 23B. Along with progress in the etching process by argon ions 25, molecules and atoms sputtered out of a slider substrate 1 build up mainly on a wall face 26 of a mask 2 such as a resist and the like, and a wall face 27 of each of the air bearing grooves 29 formed by the etching process, thus forming a redeposition layer 28.
Meanwhile, as the etching process by the argon ions 25 proceeds substantially in parallel with formation of the aforesaid redeposition layer 28, the removal of the redeposition layer 28 through the etching process hardly occurs (FIG. 23A). Consequently, when the mask 2 is removed upon completion of the etching process, parts of the redeposition layer 28 remain as "burrs" 28a, protruding from the air bearing surface 11 (FIG. 23B).
In the negative pressure cavity slider of which the flying height of 0.1 .mu.m or less is recently required the, presence of the burrs 28a as described above prevent air pressure distribution over the air bearing surface 11 from conforming to a design calculation, resulting in instability of the flying height of the magnetic head. This has caused an output of the magnetic head to fluctuate, thereby causing errors in recording and reading. Furthermore, there was even a risk of the burrs 28a damaging the magnetic disk surface, and causing such a critical failure as erasure of data recorded in the magnetic disk.
Accordingly, the conventional practice was to remove the burrs 28a by lapping the air bearing surface 11 of the slider substrate 1 using a grinder and the like after completion of the etching process. Such an additional step of processing, however, results in an increase in the production cost and a decrease in the yield because satisfactory jig positioning accuracy was not obtainable when changing over from jigs for etching to same for mechanical grinding.
During the conventional etching process, a practice of controlling generation of burrs 28a by use of the so called oblique working has also been employed, thereby rotating the slider substrate 1 at a predetermined tilt angle to the direction in which the argon ions 25 are coming in. It is an attempt to remove by etching the redeposition layer 28 building up on the wall face 26 of the mask 2 and the wall face 27 of the air bearing groove 29 by injecting the argon ions 25 obliquely.
However, when the argon ions are injected so as to strike obliquely and evenly against the wall faces 26 and 27 that are oriented in various directions by rotating the slider substrate 1, edge portions in the air bearing groove 29 are temporarily shaded from the ion bombardment depending on the tilt angle of rotation. As illustrated in FIG. 24, each of the edge portions 29a temporarily shaded makes a slope because a processing rate in this region becomes less than that for another bottom surface region 29b of the air pressure groove 29.
In designing the negative pressure cavity slider, the air pressure distribution is calculated on the assumption that the edge portions 29a of the air bearing groove 29 are properly worked. Accordingly, the aforesaid slope of each of the edge portions 29a leads to errors in the air pressure distribution, making it difficult to provide the magnetic head with the flying characteristic as expected.
A second problem as pointed out is a rate of processing by the sputter-etching method, that is, a low etching rate. Very fine composite ceramic material containing aluminum oxide (hereinafter sometimes referred to as "alumina") and titanium carbide as main constituents has lately come into wider use for making the slider substrate. The time required for processing such a composite ceramic material as described above through the etching process utilizing the effect of sputtering by argon ions becomes considerably lengthened.
In the case of processing the composite ceramic material described above by use of the ion milling process belonging to the sputter-etching method, a depthwise etching rate is normally in the order of 20 to 30 nm/min. Consequently, it took many hours to complete the negative pressure cavity slider provided with the air bearing grooves (usual depth: 5.about.20 .mu.m).
This has resulted in not only considerably lower productivity but also intense depletion of the etching apparatus due to continuous operation for many hours, necessitating frequent replacement of electrodes, filaments, and the like, thereby complicating maintenance work.
A third problem, as pointed out, is roughness of a work surface after etching. Specifically, in the composite ceramic material made mainly of aluminum oxide and titanium carbide, crystal grains of respective constituents are present in a state independent from each other. It is known that when the sputter-etching method is applied to the composite ceramic material described above, aluminum oxide grains are preferentially removed by etching. As a result, only titanium carbide grains remain on an etched surface, causing the work surface to become rough. Furthermore, as the titanium carbide grains were often in a state about to be broken away from the work surface, they posed a risk of damaging the magnetic disk surface when they were in fact broken away in the course of the magnetic head being driven in operation. In addition, there was a strong likelihood that fine debris would find their way into ragged parts of the etched surface, creating a cause for concern with unstable flying characteristic of the magnetic head.
As described in the foregoing, with the conventional method of working on the magnetic head slider with the use of sputter-etching method utilizing argon plasma, there have been pointed out such problems as protruding burrs remaining on the air bearing surface, lower productivity due to longer processing time required, the need for complicated maintenance work, and rough etched surfaces.
It is, therefore, an object of the invention to provide a method of fabricating a magnetic head slider having high reliability as well as stable flying characteristic in a short time, solving the problems as described above.